**1. Introduction**

Diseases that are caused by pathogens producing bacterial biofilms are increasingly spread, which represent a real threat to human health. Therefore, floating or

swimming bacteria are more vulnerable to antibiotics. However, they can be reorganized into clusters of very complex structure, composed of a matrix of selfsynthesized exopolymers, which forms the notorious biofilm that is hard to eradicate because bacteria embedded in this structure become highly resistant to many antimicrobial agents. In fact, when trapped in biofilms, biofilm-producing bacteria can be over 1000-fold more resistant to antimicrobials than their planktonic equivalents [1]. In addition, the massive use of antimicrobials has led to an increment in multi-drug resistance (MDR) of pathogenic bacteria, rendering the failure of antibiotic treatment. The six main multidrug-resistant and fatal pathogens are known as "ESKAPE" pathogens: *Escherichia coli*, *S. aureus*, *Klebsiella pneumoniae*, *A. baumannii, P. aeruginosa and Enterobacter* spp. These bacterial agents are responsible for polymicrobial infections that cause diseases such as cystic fibrosis, ear and urinary tract infections, respiratory tract infections, diabetic ulcers, wounds, in addition to the contamination of certain medical devices [2]. Furthermore, majority of chronic and nosocomial infections are associated with mono- or polymicrobial biofilms, having a significant impact on the survival rates of patients. Although the use of medical devices revolutionized health care services and significantly improved patient outcomes, it also led to complications due to the associations with biofilms and the emergence of multidrug resistant bacteria.

In particular, MDR bacteria poses a major challenge as current antimicrobial therapies are often associated with poor outcomes [3]. Based on the progress of the mechanism of biofilm development in MDR bacteria, many anti-biofilm molecules are being discovered with diverse modes of action such as quorum quenching (QQ) and cell adhesion inhibition, dispersion of extracellular polymeric substance, and interference with c-di-GMP signaling pathways, etc. [4]. Taking these factors into account, it is clear that new strategies are required to weaken the biofilm, inhibiting its proliferation and making it less resistant to antibiotics. These strategies involve targetting the resistance mechanisms of pathogenic bacteria like the production of biofilms by controlling quorum sensing (QS) since it is an intercellular communication system, which influences microbial virulence [5]. Therefore, interference in QS system of bacterial pathogens can reduce drug resistance which is considered as a suitable alternative that attenuates pathogenicity and protects the host from infection due to biofilm formation [1].

This issue has prompted researchers to find new microbial biofilm inhibitors that could be combined with existing antibiotics to improve their efficacy in bacterial eradication. In recent years, researchers have increasingly sought alternative therapeutic strategies for effective treatment of biofilm-producing pathogens. The target is to overcome the drawbacks of conventional antimicrobial therapies as microbial infections involving biofilms become quite challenging because of their high antibiotic resistance capacities. Within this framework, the present study has evaluated the antibiofilm characteristics of natural and synthetic molecules against MDR bacteria.

### **2. Anti-biofilm activity of peptides and organic compounds**

#### **2.1 Anti-biofilm activity of 3-Phenylpropan-1-amine (3-PPA)**

Phenylpropane-1-amine (3-PPA) is known to be an antibiotic adjuvant that interferes with QS and disrupts signaling between bacteria without posing a threat to the bacteria themselves, potentially resolving resistance in pathogenic bacteria [6]. In this recent and unique study, 3-phenylpropan-1-amine (3-PPA) was determined to inhibit biofilm formation. Furthermore, the inhibitory effect rises along with high drug

*Efficacy of Natural and Synthetic Biofilm Inhibitors Associated with Antibiotics… DOI: http://dx.doi.org/10.5772/intechopen.112408*

concentrations. Notably, at 50 μg/mL, 3-PPA treatment reduces biofilm formation by 48%. Moreover, 3-PPA probably acts on virulence factors. They also studied the expression of genes related to detoxification enzymes and found a 37% inhibition in the expression of *sodB* gene, which encodes superoxide dismutase (SOD). Given the inhibitory effects of 3-PPA on biofilm formation, they also explored whether 3-PPA can increase the vulnerability of biofilms to traditional antibiotics. Thus, biofilms were exposed to 3-PPA and antibiotics in combination. In fact, 3-PPA (50 μg/mL) or ofloxacin (0.2 μg/mL) alone had weak effects on biofilm eradication, but relatively strong effects when used in combination, with a biofilm erasure rate of 44%. They also confirmed that by scanning electron microscopy (SEM), treatment with the combination of 3-PPA and ofloxacin resulted in the significant dispersal, destruction, and reduction of the preformed biofilm. Therefore, 3-PPA was used as an antibiotic adjuvant to interfere with the QS and interrupt the signaling between bacteria while not being a threat to the microorganism, which could help solve the problem of resistance in disease-causing bacteria. This is the only work to develop a strategy to by-pass multidrug-resistant *S. marcescens* and improve treatment outcomes for recalcitrant infections (**Table 1**).

#### **2.2 Anti-biofilm activity of cathelicidin-related antimicrobial peptide (CRAMP)**

De Brucker et al. [7] identified AS10 (Peptide Sequene: KLKKIAQKIKNFFQKLVP) as the most potent anti-biofilm peptide at 0.22 M. This peptide inhibits biofilm formation of the fungus *C. albicans* and also various Gram-positive and Gramnegative bacteria in a mixed biofilm and acts synergistically with caspofungin or amphotericin B against mature *C. albicans* biofilm. Recently, in the study by Zhang et al. [8], the best synergistic activity of CRAMP combined with colistin at 62.5 μg/ml was confirmed for *P. aeruginosa*, with a significant inhibition of the biomass of preformed biofilms reaching 91.05%, confirmed by confocal laser scanning microscopy (CLSM) images. It was also confirmed that the combination (CRAMP-1/4 MIC colistin) also down-regulated the expression of QS regulated genes, including pyocyanin and rhamnolipid production [9]. In 2022, the same research team also elucidated the specific mechanism by which CRAMP was able to eradicate *P. aeruginosa* biofilms using an integrative analysis of transcriptomic, proteomic and metabolomic data [10]. Somal data showed that CRAMP acts on *P. aeruginosa* biofilms through a range of pathways, which include the *Pseudomonas* quinolone signaling system (PQS), the cyclic dimeric guanosine monophosphate (c-di-GMP) signaling pathway, and the exopolysaccharide and rhamnolipid synthesizing pathways [10]. These studies provide new possibilities for the development of CRAMP as a potentially effective anti-biofilm dispersant or even a biofilm-preventive coating for implants (**Table 1**).

#### **2.3 Anti-staphyloxantin activity of NP16 and Celastrol in** *S. aureus* **biofilm**

In the recent study by Gao et al. [11], it was demonstrated a novel inhibitor (NP16) of *S. aureus* staphyloxantin (STX) production. This inhibitor targets the dehydrosqualene desaturase (CrtN) which catalyzes the first step of the staphyloxantin biosynthetic pathway. Staphyloxantin inhibition can reduce the survival of *S. aureus* under oxidative stress conditions and limits biofilm formation. This newly discovered CrtN inhibitor NP16 may represent an effective strategy for combating *S. aureus* biofilms. This molecule is not the only one to have an anti-



**Table 1.**

*List of biofilm inhibitors.*

*Efficacy of Natural and Synthetic Biofilm Inhibitors Associated with Antibiotics … DOI: http://dx.doi.org/10.5772/intechopen.112408*

staphyloxantin activity, as the study of Yehia et al. [12] demonstrated that celastrol efficiently STX biosynthesis in *S. aureus* through its effect on CrtM efficiently, confirmed by liquid chromatography-mass spectrometry (LC-MS) and molecular docking. In addition to its anti-pigment capability, celastrol exhibits significant antibiofilm activity with its inhibitory effect on bacterial cell exopolysaccharides. Similarly, inhibition of STX upon celastrol treatment rendered *S. aureus* more susceptible to membrane targeting antibiotics. As a novel anti-virulent agent against *S. aureus*, Celastrol provides a prospective therapeutic role as a anti-pathogenic agent with multi-targets (**Table 1**).
